Reduction of contrast of photographic emulsions



June 7, 1938.

REDUCTION c. J. STAUD 2,119,724

0F CONTRAST OF PHOTbGRAPHIC EMULSIONS Filed July 10, 1935pwmbzezkummwmrwkmmzm pfif mulially I m ilzlged I 'I I I Patented June 1938 UNlTE D STATES PATENT OFFICE.

REDUCTION or CONTRAST or micro ammo Emulsions Cyril J. Stand, Rochester,N. Y., assignor, by mesne assignments. to Eastman Kodak Com pany, JerseyCity, N. J., a corporation of New Jersey Application July 10, 1935,Serial No. 30,716

2 Claims.

fact that the developer does not difiuse evenly into all portions oftheemulsion during development, but acts more rapidly on those layerslying closer to the surface than on the lower layers. Furthermore, theoxidation products resulting from the action of the developer areremoved rapidly at the surface, but diifuse much more slowly from thelower layers of the emulsion and consequently accumulate there in suchconcentration as to exert a marked restraining action on the developer.

This invention has as its principal object to provide a means ofreducing the contrast of a photographic emulsion. Another object is toprovide a means of' controlling the action of a developer on alight-sensitive photographic emulsion. A further object is to provide animproved photographic film which may be developed without an undesirabledegree of contrast in a developed image. Other objects will appearhereinafter.

These objects are accomplished by the following invention, which in itsbroader aspects, comprises applying over the outer surface of theemulsion a thin, permeable layer comprising a cellulose derivativehaving. incorporated therein a water-soluble compound readily misciblewith the cellulose derivative. I have found that'the application of sucha coating results in reducing the contrast of the image obtained ondevelopment. This result is rather surprising, especially in view ofthe'fact that the cellulose derivatives are. in general, impermeable towater and other liquids to an extent which would'lead one to theconclusion that their use in connection with the .overcoating ofphotographic emulsions would be impractical. I have found, however, thatif certain watersoluble ingredients are incorporated with the cellulosederivative, a thin coating may be produced which issuflicientlypermeable t'o permit penetration of the developer and thatthis coating has the remarkable effect of controlling the action of thedeveloper to such an extent that the contrast 'of the resulting imagemay be considerably reduced over what would be the case if such layerwere'rtot employed.

In the following examples and description I have set forth several ofthe preferred embodiments of my invention, but it is to be understoodThis invention relates to photographic matethat they are included merelyfor purposes of illustration and not as a limitation thereof.

In the accompanying drawing in which like reference characters refer tolike parts,

Fig. 1 is a section through a photographic film embodying my invention,.the thickness of the various layers being greatly exaggerated forclearness of illustration;

Fig. 2 is a section through another type of pho tographic product inaccordance with the invention illustrating the use of water-permeablelayers both over and between the various emulsion. layers of a filmcomprising a plurality of emulsion layers. A I

The cellulose derivative employed may be a simple cellulose ester-suchas cellulose nitrate, cellulose acetate, cellulose propionate, a mixedester, such as cellulose acetate nitrate, cellulose acetate propiona-te,or a cellulose ether. Many other similar compounds willsuggestthemselves to those skilled in the art. In accordance with my inventionthe cellulose derivative is applied in the form of asolution of ratherlow concentration, since only an extremely thin layer of the materialshould be laid down on the emulsion. Otherwise it would require anexcessive length of time for the developer to penetrate the coating thusproduced. In order to provide for the necessary degree of permeabilityof the. celluloseQde-v rivative layer, I mix with the cellulosederivative solution a water-soluble material e'asily miscible therewith.This material must conform to certain requirements, namely, it mustnot-inhibit adhesion of the cellulose derivative to the emulsion, itmust be compatible with the cellulose de rivative and with the emulsionand must'besoluble, both in water and in the solvent orsolventcombination employed for dissolving the cellulose derivative.

= materials which I have found useful for the pur- Typical examples ofwater-soluble 40 poses of my invention are certain water-solublecompounds. including mono-acetin, the compesi tions manufactured andsold by the Glycol Prod ucts Company of New York,.Nw Y0rk, under thetrade names; Glycol Bori-Borate and Glyceryl Bori-Borate and certainother compounds suchas sucrose, dextrin, starch acetate and'pyridine ni-I v Example I f 5 grams of cellulose "acetate and 2 grams ofm'o'noacetin are-dissolved in '100 cc. of ethylene chloride, 9 parts,and ethanol 1 part, producing a 5% solution. This-solution is applied inany .well known manner to the surface of a moderately derivative coatingover the emulsion has marked;

ly reduced the contrast of the original ,e'mulsion.

' Example II grams of Glyceryl Bori-Borate are dissolved in 100 cc. ofacetone solution. This solution is applied in any well known manner tothe surface of a moderately high contrast emulsion previously coated ona suitable film support. A' second emullayers maybe of differentialsensitivity characteristics. Upon exposing, developing, fixing andwashing the film itis found that a negative of a highly satisfactorydegree of contrast is produced, the permeable cellulose derivativelayers over the emulsion layers providing a means of controllingcontrast the action of the developer thereon similarly to the singleemulsion layer film of Extains about.50% by weight of the cellulosederivative material, the remaining 50% consisting of the water-solublematerial. I have also found that the most satisfactory results areobtained when this 50- 50 mixture is dissolved in the solvent to producea .5 to solution. As previously indicated, it is necessary to userelatively dilute solutions in order that the cellulose derivative layerlaid down on the. emulsion shall not be too thick, as this wouldundoubtedly increase the time of "development and subsequent processing.As will be readily appreciated the thickness of this layer. is a matterwhich can vary widely, but in any event the layer will probably not bemore than 20 to 50 microns in depth.

Although I do not restrict-myself to the use of any particular solvent,water-soluble component or cellulose derivative, nor to any particularconcentration of the coating solution, I find that the more satisfactoryresults are obtained with the relatively volatile solvents and the useof concentrations of dissolved components of not over 5%.

My invention will be more clearly understood by reference to theaccompanying drawing in which the numeral I (Fig. 1) represents asupport such as a glass plate, a cellulose derivative film, or the like.The numeral 2 designates a itable light-sensitive gelatino-silver halideemulsion, while the numeral .3 designates a thin, permeable celluloseester layer having incorporated therewith in accordance with myinventiona .water-soluble component, such as monoacetin.

result is that all of the exposed grains of the sensitive silver halideare acted upon more uniformly throughout the various strata of theemulsion and 'for a more nearly equal period. It follows that, since theoxidation products of development are more uniformly distributed, thetendency toward accumulation ofsuch prodnets in rather hi hconcentrations in the, upper layers of the emulsion (as is thecase withemulsions which are not provided with such coatings) Y is reduced. oreliminated. This makes possible a 5 grams of cellulose acetatepropionate and 2.5

fairly uniform removal of such products throughout the" emulsion in thefixing and subsequent operations, and results in a fairly markedreduction of contrast as compared to emulsions which are not treated asdescribed herein.

In the film structure illustrated in Figure 2, the numeral I designatesany suitable .cellulose derivative film support, such as one composed ofcellulose nitrate or cellulose acetate. The m1- merals 2 and 4 designatemoderately high contrast emulsion layers of differential sensitivity,while the numerals 3 and 5 designate, respectively, a layer of cellulosederivative material containing a miscible, water-soluble component, suchas monoacetin, Glycol Bori-Borate, sucrose, dextrin or other compatiblewater-soluble material, and a similar cellulose derivative layercontaining these componentssuperimposed on the'upper emulsion layer. Asin the product of Figure 1, the permeable cellulose derivative layersprovide a means of controlling the eflect of the developer on thedifferent light sensitive emulsion layers, reducing the contrast of theoriginal emulsion.

It will be evident from the above examples that the percentage of thewater-soluble material in the permeable layers may be varied to, conformto varying emulsion requirements. For example, if a more permeable layeris required the percentage of water-soluble component will be'increased,and vice versa.

Although I have referred herein principally to the effect of thecellulose derivative coating in reducing the contrast of the emulsion,such coating has the additional advantage that it serves to some degreeas a protective coating and reduces the possibility of damage-to thefilm be-' cause of scratches, abrasions and the like. y- What I claimis:

1. In the process of developing the latent image '.by subjecting theexposed film to the action of a developer, the step which comprisescontrolling the contrast of the image by controlling the rate anduniformity of diifusion of the developer into the emulsion layer bycoating the surface of the emulsion layer with an extremely thin,permeable, permanently adherent, sistant, cellulose derivative layerwhich is insoluble in the presence of alkaline developing solutionsand'containing a water-soluble and ,displaceable compound in sumcientamount to permit penetration of the layer by the developer bydisplacement of the water-soluble compound, whereby the action of the'developer on the lightsensitive emulsion is rendered substantiallyuniform throughout.

2. A photographic film comprising a support layer, a light-sensitivegelatino-silver halide emulsion coated on the support and means for Ycontrolling the contrast of a latent image in the emulsion layer upondevelopment by controlling the rate and uniformity of diffusion of thedeveloper into the emulsion layer, said means comabrasion-reprising anextremely thin, permeable, permanent- 1y adherent, abrasion-resistant,cellulose derivative layer which is insoluble in the presence ofalkaline developing solutionsand containing a water-soluble anddisplaceable compound in sufficient amount to permit penetration of thelayer by the developer by displacement of the watersoluble compound,whereby the action of the developer on the light-sensitive emulsion isrendered

